This invention relates to screening apparatus for use in size classifying discrete material. Heretofore, screening apparatus has been provided of the type having a screen box with an upstanding surround within which one or more vertically-spaced stations have been provided each to horizontally carry an elongate screening surface. The action of size classifying material passed into the screen box is effected by vibratory, reciprocatory, or oscillatory means. The or each screening surface has engaging means at longitudinally opposite ends each to be secured to a holding member arranged transversely, one at each longitudinally opposite ends of the station. Desirably, but not essentially, one holding member is fixed and the other holding member is movably adjustable to allow longitudinal tensioning or releasing of a respective screening surface. Replacing worn screening surfaces or changing screening surfaces to give a different grade(s) of material on existing screening apparatus of the above type is time consuming particularly, but not only, in the tensioning aspect of the replacement screening surfaces and this is disadvantageous.